The invention relates generally to an arrangement for regulating the introduction of substances into chambers. Of particular interest to the invention is the introduction of particulate materials into chambers, and especially the feeding of coal into coke ovens.
A known arrangement for measuring and regulating the level of coal in coke ovens includes one or more pressure of sensing tubes which extend into an oven chamber or chambers. A predetermined gas pressure is maintained in such a pressure tube by passing a gas therethrough. A pressure switch is connected with the pressure tube and the pressure switch is, in turn, electrically connected with a switch for the transporting device which conveys the coal to the coke oven. The arrangement just described operates to pneumatically measure and regulate the level of the coal in the coke oven.
The pressure of sensing tube has an end located in the coke oven chamber at a predetermined level of the latter and, as indicated above, a certain gas pressure is maintained interiorly of this tube. The measuring principle of pneumatic devices for determining the filling level in coke ovens is generally based on the fact that the moist or preheated coal blocks the end of the sensing tube to at least some extent when, during the filling operation, the level of the coal reaches the level at which the end of the sensing tube is located. As a result, the gas flowing through the sensing tube which may, for instance, be air, is prevented from freely entering the coke oven chamber, that is, the flow of the gas is restricted at the outlet end of the sensing tube. This causes a backpressure to be generated, that is, this causes a pressure increase interiorly of the sensing tube.
A certain gas flow quantity is required in order that a pressure increase may be associated with the abovementioned blockage of the sensing tube. In addition, the end of the sensing tube must be immersed in the coal charge to a certain predetermined extent.
The pressure increase which may be achieved interiorly of the sensing tube is limited inasmuch as the charge surrounding the end of the sensing tube does not completely seal the sensing tube. Thus, only a certain, limited resistance to flow will be achieved for a given depth of penetration of the end of the sensing tube into the coal charge and gas will continue flowing out of the sensing tube into the coke oven chamber even after the end of the sensing tube is immersed in the coal charge. Upon exceeding a relatively low backpressure, for instance, a pressure corresponding to a water column of 100 millimeters where preheated coal is being charged, the gas pressure becomes sufficient to blow the end of the sensing tube free of coal and to thereby permit the gas, e.g., air, to freely flow into the coal charge. The critical pressure increase is still lower where moist coal is being charged. Here, the pressure corresponds to a water column of only about 20 millimeters. The low pressure increase achieved in the sensing tube, which pressure increase may also be referred to as the switching pressure, must suffice, when in the form of an impulse, to activate the subsequent switching operations such as, for example, those terminating the filling operating. For terminating the filling operation, the pressure increase must suffice to activate the abovementioned pressure switch which, in turn, operates the switch provided for the transporting device which conveys the coal to the coke oven.
The reason why the critical pressures for moist and preheated coals are different resides in that the bulk density of moist coal differs from that of preheated coal. The difference in bulk density is associated with the fact that the free spaces between the individual coal particles are of different size for moist and preheated coals. As a result, different pressures will be generated in a sensing tube for a given gas quantity, the pressure in the sensing tube corresponding to the bulk density of the coal being charged. A high bulk density results in a higher pressure and vice versa.
The measuring devices of the above type, which are intended to provide signals for the orderly filling of coke oven chambers via small regulating impulses as just described, possess certain disadvantages. A particularly severe disadvantage resides in the fact that pressure waves are generated in the coke oven chamber during the filling operation, especially at the beginning of the filling operation. These pressure waves are caused by the coal which is being charged into the coke oven chamber. The pressures associated with the pressure waves are of about the same magnitude as the switching pressures and, accordingly, the pressure waves do not only disturb the measuring procedure but make it impossible to carry this out.
Another disadvantage is associated with the fact that a certain predetermined quantity of gas, e.g., air, must be conveyed through the sensing tube in order to guarantee that the requisite pressure increase, that is, the switching pressure, is achieved. This requires that the supply pressure for the gas be adjusted to a level which approximates the magnitude of the switching pressure itself. As a result, the measuring procedure is made difficult, if not impossible, to carry out.